This invention relates to the conditioning of seeds, such as for example, by priming, chemical treatment and biological treatment and to the use of biologically treated seeds to recondition land and improve plant productivity.
Seed priming or osmoconditioning are terms to describe a known pre-sowing hydration treatment developed to improve seedling establishment (Heydecker and Coolbear, 1977, Seed Science and Technology 5:353-425), (Khan, et al., 1980/81, Israel J. Bot. 29:133-144) and (Bradford, 1986 HortScience 21:1105-1112).
In seed priming, the seeds are placed in an aerated osmotic media of known water potential. In this process, the osmotic solutions induce a water potential that prevents the completion of germination (radicle emergence). Seeds are, however, able to imbibe and complete the early phases of germination under limiting water content conditions. The duration of the priming treatment has been reported to be from less than 24 hours (Guedes and Cantliffe, 1980, J. Amer. Soc. Hort. Sci. 105:777-781) to several weeks (Khan, et al., 1980/81, supra) and is dependent on species, cultivar and even seedlot. Seeds are then dried back. After priming, seeds can be sown with existing planters. Results obtained from priming different crop seeds have been reviewed by Bradford, 1986, supra. In general, seedling emergence of primed seeds is earlier and more sychronous than dry sown seeds. Improvements in plant growth and yield characteristics have also been documented.
In the prior art priming processes, several different osmoticums have been used to achieve the water potential for priming including high molecular weight (MW of 6000-8000) polyethylene glycol (PEG) and/or inorganic salts (Heydecker and Coolbear, 1977, supra). After priming, the seeds are removed from the solution used for establishing the water potential before being dried back.
Several technical and logistical difficulties have been encountered with the prior art priming techniques. For example, osmotic solutions require continuous aeration and in general, a large volume of priming solution is required per quantity of seeds. Reductions in percentage seedling emergence have been reported with the use of inorganic salts (Brocklehurst and Dearman, 1984, Ann. Applied Biol. 102:585-593). A relatively high concentration of PEG in solution is viscous and has low oxygen solutibility and diffusivity (Mexal, et al., 1975, Plant Physiol. 55:20-24).
An alternative to the use of solutions is to prime seeds in a solid medium. A solid material should have a high water holding capacity and allow seeds to imbibe. Peterson (1976, Sci. Hort. 5: 207-214) described a procedure to prime onion seeds in a slurry of PEG 6000 and vermiculite. A ratio of three to four parts vermiculite moistened with PEG solution were mixed with one part seed. Although this technique overcame the need for aeration, he reported that the seeds were difficult to separate from the vermiculite. Methods have been described to increase the seed moisture content of large-seeded vegetables prior to sowing (Bennett and Waters, 1984, J. Amer. Soc. Hort. Sci. 109:623-626 and 1987, J. Amer. Soc. Hort. Sci., 112:45-49). Seed moisture content of lima beans (Phaseolus lunatus) and sweet corn (Zea Mays) was increased by combining seed, vermiculite and a known amount of water in a closed container. This mixture was incubated and then the vermiculite sieved away prior to sowing the hydrated seed. Seedling establishment was improved by the pre-sowing treatments for both crops.
Inoculation of seeds with bacteria or chemicals prior to planting is known in the art. For example, United Kingdom patent specification 849,210 discloses inoculating seeds under reduced pressure to enable penetration of the bacteria under the coat of the seed and thus survival of the bacteria for a period of time. This procedure is expensive and appears to be limited in the range of bacteria that can be inoculated into seeds.